In the manufacture of cast iron engine V-blocks, a so-called integral barrel crankcase core has been used and consists of a plurality of barrels formed integrally on a crankcase region of the core. The barrels form the cylinder bores in the cast iron engine block without the need for bore liners.
In the sand casting process of an aluminum internal combustion engine cylinder V-block, an expendable mold package is assembled from a plurality of resin-bonded sand cores (also known as mold segments) that define the internal and external surfaces of the engine V-block. Typically, each of the sand cores is formed by blowing resin-coated foundry sand into a core box and curing it therein. Cast-in-place bore liners are often used in such castings.
Traditionally, in the manufacture of an aluminum engine V-block with cast-in-place bore liners, the mold assembly method involves positioning a base core on a suitable surface and building up or stacking separate mold elements to shape such casting features as the sides, ends, valley, water jacket, cam openings, and crankcase. The bore liners are positioned on barrel cores such that the liners become embedded in the casting after the metal is poured into the mold. Additional cores may be present as well depending on the engine design. Various designs for the barrel cores are used in the industry. These include individual barrel cores, “V” pairs of barrel cores, barrel-slab cores, and integral barrel crankcase cores. The barrel-slab and integral barrel crankcase designs are often preferred because they provide more accurate positioning of the liners within the mold assembly.
The engine block casting must be machined in a manner to ensure, among other things, that the cylinder bores (formed from the bore liners positioned on the barrel features of the barrel cores) have uniform bore liner wall thickness, and other critical block features are accurately machined. This requires the liners to be accurately positioned relative to one another within the casting, and that the block is optimally positioned relative to the machining equipment.
The position of the bore liners relative to one another within a casting is determined in part by the dimensional accuracy and assembly clearances of the mold components (cores) used to support the bore liners during the filling of the mold. Another important consideration is the ease and consistency with which the liners are brought into the desired final position during the mold assembly process. The final positioning of the liners during mold assembly is often facilitated by the use of angled seats in the mold that engage with mating chamfers on the inner diameter at each end of the liners. The force required to achieve this final engagement of the tapered seat into the liner chamfer can be substantial, especially in V-type casting molds, resulting in damage to the sand seats and/or failure to fully engage said seat into the liner chamfer.
It would be desirable to produce a core for sand casting of engine cylinder blocks wherein a dimensional accuracy in the positioning of cast-in-place bore liners is maximized.